The invention relates to friction generating and friction-operated devices in general, and more particularly to friction rings, friction generating pistons and analogous parts (hereinafter called friction elements) which can be utilized in various types of friction clutches, for example, in so-called lockup clutches or bypass clutches of the character employed in the housings of hydrokinetic torque converters.
It is well known to utilize friction rings, friction linings and analogous friction elements in so-called wet running clutches wherein the friction elements should establish one or more paths for the flow of a cooling fluid (e.g., oil) between compartments, wherein the fluid is maintained at different pressures. To this end, the friction elements have friction faces provided with channels for the flow of fluids between such friction faces and the complementary friction faces that form part of wet running clutches. For example, the axially reciprocable piston of a wet running lockup clutch in a torque converter can be provided with a friction lining constituting a first friction element, and the housing of the torque converter can be provided with a second friction element having a friction face which is contacted by the friction face of the first friction element when the lockup clutch is engaged. At least one of the two friction faces is or can be provided with one or more channels serving to establish one or more paths for the flow of a fluid coolant between the two compartments that form part of the internal chamber of the housing of the hydrokinetic torque converter and that contain bodies of fluid which are maintained at different pressures. Adequate cooling of the friction linings and/or analogous friction elements is particularly important when such friction elements are utilized in lockup clutches of the type wherein one of the friction elements is compelled to turn relative to the other friction element even in the engaged condition of the lockup clutch.
Reference may be had, for example, to U.S. Pat. Nos. 4,969,543 and 5,056,631 which disclose hydrokinetic torque converters with wet running lockup or bypass clutches. Each of these patents discloses lockup clutches wherein the cooperating friction faces are configurated in such a way that they permit a coolant to flow between a first compartment containing a fluid at a relatively high pressure and a second compartment containing a body of fluid at a relatively low pressure; such flow of fluid between the two compartments and by way of one or more channels can take place while the lockup clutch is engaged to transmit torque between the rotary housing of the hydrokinetic torque converter and the hub of a turbine in the housing.
A drawback of conventional lockup or bypass clutches and of their friction elements is that they fail to ensure adequate cooling of the components of such friction clutches under all circumstances of use, including the operation of the lockup clutch with a certain amount of slip while the clutch is maintained in the engaged condition. Overheating of component parts of a lockup clutch shortens the useful life of the clutch as well as of the torque converter in which the clutch is put to use.